The invention relates to a steam generator used in a steam generator of a pressurized water nuclear plant.
In a pressurized water nuclear power generating plant a reactor core which is disposed within a reactor nuclear vessel is cooled by primary cooling water. The primary cooling water, heated by the nuclear energy emitted from the reactor core, is introduced into a steam generator. Within the steam generator, the heat is transferred to secondary cooling water to boil the secondary cooling water. The steam thus generated drives a steam turbine to generate electric power. The steam generated within the steam generator is introduce into a steam separating device, disposed in upper inside volume of the steam generator, for removing the water contained in the steam flow. The steam separating device generally comprises centrifugal steam separators disposed at the upstream side relative to the steam flow and a frame plate type moisture separator disposed at the downstream of the centrifugal steam separators.
FIG. 5 shows an example of the conventional frame plate type moisture separator.
In FIG. 5, a moisture separator 10 comprises a plurality of frame plates 12. A plurality of zigzag passages 11 are defined between the frame plates 12. Each of the frame plates 12 for defining the passages 11 includes a plurality of droplets collecting pockets 14 disposed side wall portions 12a extending from roots 16, which swell outwardly relative to the zigzag passage 11, toward apexes 18 which swell inwardly relative to the passage 11. The steam including droplets W is supplied into the passages 11 through the left ends, in FIG. 4, and discharged through the right ends after the droplets W are trapped and removed into the pockets 14.
Recently, reduction in moisture at the outlet of the steam generator is required. However, there is a problem that the conventional moisture separator 10 cannot reduce the degree of wetness sufficiently. That is, the conventional moisture separator 10 has a problem that the droplets collecting pockets disposed at the upstream sides in the passages 11 can collect relatively large droplets W, however, so called carry over occurs so that the droplets that were once trapped by the pockets 14 fly out of the pockets into the stream flow in the passage 11 or the relatively small droplets W cannot be trapped sufficiently by the pockets 14 disposed at the downstream side in the passage 11.
The invention is directed to solve the above described problems of the prior art and to provide a moisture separator improved to increase the droplets collection performance.
Further, the objective of the invention is to provide a moisture separator which reduces its production cost.
Further, the objective of the invention is to provide a moisture separator which can collect relatively small droplets.
According to the invention, there is provided a moisture separator comprising a plurality of flat frame plates disposed parallel to each other to define a plurality of zigzag passages between the frame plates, side walls facing the upstream side of the passages defining entrance openings of droplet collecting pockets.
The production cost is remarkably reduced compared with moisture separators according to the prior art by using flat frame pieces.
According to the invention, there is provided a moisture separator with a plurality of frame plates disposed parallel to each other to define a plurality of zigzag passages, wherein the frame plates comprise flat plate members; the moisture separator comprising droplet collecting pockets having entrance openings disposed in side wall portions of the zigzag passages between, seeing from the upstream side of the passages, roots swelling outwardly relative to the passage and apexes swelling inwardly relative to the passage; and the droplet collecting pocket including first droplet collecting pockets, disposed at the upstream side of the passages, for collecting relatively large droplets, and second droplet collecting pockets, disposed at the downstream side of the passages, for collecting relatively small droplets.
When the steam flows through the zigzag passages, the droplets contained in the steam impinge against the side walls of the passages. At that time, a portion of the droplets enters the droplet collecting pockets and are trapped in the pockets. At the upstream side of the passages, relatively large droplets are collected because large droplets are easily trapped. Therefore, the first droplet collecting pockets for collecting relatively large droplets are disposed at the upstream sections of the passages. On the other hand, in the downstream sections of the passages, relatively small droplets stay still in the steam flow after the large droplets are trapped. Therefore, the second droplet collecting pockets for collecting relatively small droplets are disposed at the downstream sections of the passages. Hence, the droplet collection efficiency in particular the collection efficiency for the small droplets can be remarkably increased by the arrangement of the first droplet collecting pockets for collecting relatively large droplets disposed at the upstream sections and the second droplet collecting pockets for collecting relatively small droplets disposed at the downstream sections of the passages.
The entrance openings of the first droplet collecting pockets are preferably disposed apart from the apexes in the side wall portions between the roots swelling outwardly relative to the passage and the apexes swelling inwardly relative to the passage, and the entrance openings of the second droplet collecting pockets are preferably disposed adjacent the apexes in the side wall portions between the roots swelling outwardly relative to the passage and the apexes swelling inwardly relative to the passage.
Means for agglomerating droplets may be disposed between the first and second droplet collecting pockets. The means for agglomerating droplets may comprise a coil member disposed to across the passage.
Further, according to another feature of the invention, there is provided a moisture separator with a plurality of frame plates disposed parallel to each other to define a plurality of zigzag passages, wherein the frame plates comprise flat plate members; the moisture separator comprising a plurality of droplet collecting pockets having entrance openings disposed in side wall portions of the zigzag passages between, seeing from the upstream side of the passages, roots swelling outwardly relative to the passage and apexes swelling inwardly relative to the passage; and the entrance openings of all the droplet collecting pocket being disposed adjacent the apexes in the side wall portions between the roots swelling outwardly relative to the passage and the apexes swelling inwardly relative to the passage.
Furthermore, according to another feature of the invention, there is provided a moisture separator with a plurality of frame plates disposed parallel to each other and a plurality of arcuate sections attached to the frame plates to define a plurality of serpentine passages, wherein the frame plates comprise flat plate members; and the moisture separator comprising a plurality of droplet collecting pockets having entrance openings disposed in side wall portions of the serpentine passages between, seeing from the upstream side of the passages, roots swelling outwardly relative to the passage and apexes swelling inwardly relative to the passage.
Furthermore, according to another feature of the invention, a steam generator which comprises one of the above-described moisture separator, an inversed U-shaped tube bundle which uses the primary cooling water from a nuclear reactor as a heating medium and a plurality of steam separators. Steam containing less moisture can be generated by a steam generator with the above-described moisture separator so as to effectively prevent erosion at a turbine unit of a turbine generator.